Current production scanners with an automatic document feeder limit the types of documents that can be fed and imaged correctly. For example, if a document has a hole or tear, it may jam or cause multiple images when a single image is desired. Also, if a document has a cutout, making an “L” shaped document, current production scanners often feed the next document too early resulting in a truncated part of the document in the image or including part of the next document in the current image. In another example, a document with perforations, typically on a edge of the document, confuse sensors and processor algorithms and may cause a jam condition. Also, documents fed at extreme angles normally result in images missing part of the document such as truncated corners. A similar result would occur for triangular or folded documents. These kinds of document feed problems cause malfunctions of automatic document scanners.
Prior art attempts to solve these problems have included use of multiple sensors to detect the leading edge or the trailing edge of documents passing through the scanner. These sensors may be located in a line so that if any of the sensors detect an edge of a document, even if the document is tilted, a controller for the scanner starts image capture and turns off the transport feed mechanism. Multiple sensors, however, add to the cost of the scanner. It would be advantageous to minimize the number of sensors used for document detection and at the same time compensate for document cutouts, holes, and other problems described above.